DC-DC converters which generate an output voltage which is stabilized by an input voltage are known. A variety of systems may be considered as methods of stabilizing the output voltage of a DC-DC converter. For example, Patent Document 1 mentions a switching DC-DC converter which uses a PWM (pulse width modulation). The PWM system is able to stabilize the output voltage by making the switching frequency constant and adjusting the ON pulse width. There are also switching DC-DC converters which employ a comparator system. A comparator system is able to stabilize the output voltage by using a comparator to make the ON pulse width constant and adjust the OFF pulse width (that is, the switching frequency).
This DC-DC converter can be used as a voltage source such as a PU (Processor Unit). In a PU, the consumed current increases suddenly when moving from a standby state to a processing state. When the output voltage drops suddenly as a result of a sudden increase in the load current, a comparator-system DC-DC converter immediately outputs the ON pulse. Hence, in comparison with a PWM system which is unable to output a pulse during a predetermined OFF-pulse period, the output voltage stabilizes rapidly. Thus, the comparator system possesses the characteristic that the response characteristic with respect to a sudden increase in the load current is favorable in comparison with that of a PWM system.
[Patent Document 1] Japanese Patent Application Laid Open No. 2000-287439.